Re-using steel beams that have been cut with an oxy or plasma torch

[jsharkbait]

I have a project where there is a lot of temporary shoring and bracing in the form of W8 sections (these have been designed by another engineer). I've been specifying some new steel beams recently and the contractor asked if they could somehow re-use the shoring steel once it was taken out. I'd love to do this mostly for the environmental impacts, but those beams are typically much longer and so would have to be cut to the proper length onsite with a torch. I'm trying to quantify what effect this would have on the steel. The W8 sections are much more than I'd actually need and so I don't expect to load them close to the yield stress at their midspan so my concern is more with the properties of the steel at the end of the beam where it has been cut- for shear, and for any new boltholes. I imagine there could be a loss of properties somewhat or maybe some brittleness issues?

Has anybody tried to do this before or knows of what happens after cutting?

 

[XR250]

Right or wrong, I would've never given this a second thought. I'm sure it happens all the time without us knowing about it.

 

[SlideRuleEra]

Agree with XR250. As a bridge contractor, we had our own A36 non-compact beams (actually HP12x53, used as beams) for temporary forming the bottom of flat-slab bridge spans. We would field cut those beams "short" for one job then splice them back together "long" for the next... many cycles. I chose to limit bending stress to 19.6 KSI; allowable for new A36 steel is 22 KSI. Never had a problem.

http://www.SlideRuleEra.net

 

[WARose]

With any kind of torch, I don't give adjusting any allowable stresses much thought until it is has been cut/welded in the same area more than about twice. (Unless fatigue is involved.)

 

[rb1957]

is that the concern, thermal cycling ? cutting with a plasma torch, then welding on installation ?

another day in paradise, or is paradise one day closer ?

 

[phamENG]

A992 is a carbon steel and is not typically heat treated, quenched, or hardened. As long as they make clean cuts and use a drill for bolt holes, I don't think I'd worry about it.

 

[Enable]

I read your post as if you were trying to steal my identity. Literally have a bazillion W8x18s / W12x35s kicking around from temp works and repurposing them to suit. Below is a picture from today trying to do just that! Note the cut ends (torched off from previous angle connection)

I wouldn't have ever considered this to be an issue. Though, if the demand gets to the point where you'd like to consider it (I donnu say over 50% of shear at connection) then just specify that they cut them with a reciprocating blade. It sounds goofy...they will laugh and say cant be done....I know because I said that to the guys that told me that's how they were going to cut H-piles in my perimeter lagging. Sure enough, with metal blades it'll work just dandy on relatively smaller beams.

 

[Ron]

Not an issue. Flame cutting is acceptable.

 

[dhengr]

Jsharkbait:
As with many of the questions here on E-Tips, this problem requires a bit of engineering
judgement and experience, some imaginerring, and a willingness of the contractor to reward you for your effort in saving him some money. As SRE suggests, there are contractors who might buy those beams for something above scrape value, to add to their inventory of materials for shoring, forming and bracing, in their normal work process. They won’t accept junk, so your contractor has to inspect, maybe disqualify some damaged beams, and offer some assurance/guarantee that the beams are in good condition and of such-n-such spec., etc. He may have to do some weld repair, etc. on some beams to make them acceptable; that is grind off welds, fill gouges, and bolt holes, etc. There should be no permanent deformations, suggesting that the members had been over stressed. None of this should be at your liability, this is btwn. the two contractors. You may be advising what defects must be repaired and what is unacceptable.

As for reusing the beams in another structure of your design, the acceptability criteria should go up a notch, and it should be made clear that any problems with this group of beams in the final structure goes directly to the original contractor and his inspection/QC process, not to you. This should not be a random beam here and there, where you have no control or traceability of the used beams, and their final location and useage. This isn’t some sort of a hatchet job, on which you assume responsibility, to save the original contractor a few bucks in structural materials. An oxy or plasma cut beam should not be a significant problem, in and of itself, when used in the right detail, and done in a quality manor, and cleaned up after cutting to length. Examples; the cut end is in a conc. or masonry pocket in a wall, where it won’t be seen, and there is no intent to deceive. Alternatively, I wouldn’t allow just anyone to flame cut two beam ends and butt them together to make a CJP weld at midspan on a beam. There are portable bandsaw/hacksaw and mag. drills which allow field fab. work. If the original contractor wants to reuse these beams, he must inform you of any deviations from direct from the mill materials, and he must compensate you for the time needed to make an informed determination of the acceptability of the actual conditions. We have flame cut material for ages, without giving a second thought to any reduction in strength or cap’y., but this has to involve quality layout and cutting, not some guy cutting up ship parts for scrap.

 

[Tomfh]

Flame cutting is ok. Bolt hole edge distance needs to be increased slightly.

Flame cut bolt holes can be a problem….

 

[Lomarandil]

Agreed, I'll be cautious about flame cut bolt holes in high demand situations, but otherwise no issue for typical applications.

----
just call me Lo.

 

[jsharkbait]

Appreciate everybody’s thoughts on the matter! Thanks